I have a tyre in Blender: when I see it as "source files" - it is made of several smaller parts - it looks OK: enter image description here

But when I export it (dae or obj) and reimport it with the original files disabled (that is they are not seen) the imported model has some strangely shaded faces around the inner ring of the tyre. enter image description here

Can anyone explain to me why or even better provide a solution to this, please?

Here is my test blend file:

  • $\begingroup$ I did follow up on your comment, eventually.. @moonboots has nailed it for you. :) $\endgroup$
    – Robin Betts
    Commented Sep 30, 2023 at 7:49

1 Answer 1


First, you have overlapping vertices so you need to Merge by Distance. Also,you have bad split normals, select these face rings and AltN > Reset Vectors. Now select the edge loops that were marked sharp and CtrlE > Mark Sharp again.

  • $\begingroup$ I cannot clear custom split normals as it change the overall shading that I cannot recreate by simple autosmooth angle value. What I need is some sort of solution aimed speciicaly at the specific faces in that inner ring, something like Data Transfer modifier but I am unable finding the right way how to do it. $\endgroup$
    – fafa
    Commented Sep 29, 2023 at 13:24
  • 1
    $\begingroup$ Can't you just merge by distance then select these face rings and Alt N > Reset Vectors? You'll just need to redo a Ctrl E >Mark Sharp $\endgroup$
    – moonboots
    Commented Sep 29, 2023 at 13:29
  • $\begingroup$ yes, that actually made the trick: 1.) Merge vertices by distance first so no overlaps exist which basically autoclear the sharp edges there automatically (well at least in this case), 2.) select those inner ring wrongly shaded faces and Reset Normals, 3.) reselect the edges of the inner ring and make them sharp edges, done! I did not know about Reset Normals so I learned something new today again, thank you. In case you update your answer like I described here I will make your answer the correct one. ;-) $\endgroup$
    – fafa
    Commented Sep 29, 2023 at 13:45
  • $\begingroup$ I've edited my answer, is this what you want? $\endgroup$
    – moonboots
    Commented Sep 29, 2023 at 15:01
  • $\begingroup$ Basically yes, tho you could add as the first step merging by distance, not as last as it would erase those already assigned sharp edges, but OK. :-) $\endgroup$
    – fafa
    Commented Sep 29, 2023 at 15:40

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